Data regarding the television viewers research are nowadays very often gathered by automatic monitoring systems. These devices comprise sensors (or probes) on the individual appliances which report the operating condition to a central monitoring station. There exist probes which directly determine the adjustment of the tuners of a television set (abbreviated: TV) or of a video recorder (abbreviated: VCR) and furthermore determine the television programme actually tuned in through a list of locally receivable television stations. These probes, however, have to be adapted to the particular appliance, and this is extremely expensive in view of the great variety of today's appliances.
One object of the present invention is to provide a method and a device for automatically determining the condition of a video installation which does not need any intervention in the monitored appliances.